Our Research
The Problem: purifying water for drinking at near-zero degrees Celsius (32 degrees Fahrenheit), in Northern Canadian communities. Water in these communities is a dark brown colour, which is caused by dissolved organic matter. Normally, the water would be purified by mixing in a coagulant, which would bond the particles together, and then allowing these particles to settle. However, due to the colder temperatures, the coagulant's efficacy drastically decreases, making it nearly impossible to treat water at these temperatures.
The Process
Step 1: Fill the beakers with 1°C water
This water was cooled in the fridge
Explaination
The machine seen in the video is a flocculator, and it has six 2.3 litre containers that have a mechanical mixer with an adjustable speed. The coagulant (SternPac) added causes a charge between the microscopic particles of suspended colour. After the coagulant is added, a flocculator (the machine in the photos above) mixes it in, and the particles then agglomerate to form snowflake-like particles that are called flocc. The floc bonds the dirt and colour particles together and allows it to settle to the bottom. Then, after the flock has settled, the water is drained from the top of the container. The clarity of the water will be measured by a colour meter. This experiment used different dosages of coagulant to find the most effective dosage in near freezing water.
Beaker | Water Temperature (°C) | Coagulant (ml) | Coagulant Dosage (mg/L) | Apparent Colour Units: Raw Water | Apparent Colour Units: Treated Water |
|---|---|---|---|---|---|
1 | 1.0 | 0.12 | 20 | 201 | 42 |
2 | 1.2 | 0.36 | 60 | 201 | 24 |
3 | 1.2 | 0.60 | 100 | 201 | 14 |
4 | 7.0 | 0.12 | 20 | 201 | 23 |
5 | 7.0 | 0.36 | 60 | 201 | 12 |
6 | 7.2 | 0.60 | 100 | 201 | 7 |
The first 3 beakers were at near-freezing temperatures, and the last 3 were at a cool but more common and warmer temperature.
The results prove our assumption that the water at around 1°C is far more difficult to treat. The results clearly show that the apparent colour units for the water at around 1°C were roughly double that of the water at around 7°C; therefore, the coagulant was half as effective for the water at around 1°C.
From the dosages of coagulant for the water at around 1°C, the 100 ml/L was the most effective as it produced the treated water with the lowest apparent colour units.
Challenges
The biggest challenge this project faced was ensuring that the water remained at a consistent temperature. Our first solution was to move the flocculator into an industrial-sized fridge that would be cooled to one degree celsius. However, the fridge was unable to reach cold enough temperatures. The final solution was to cool the water in the fridge and to use 32 ice cubes to keep the water at a stable temperature. These ice cubes were frozen at -18°C and were made of water with the same concentration of tea to ensure that they did not dilute the water in the beakers.
Conclusion
The Clear As Ice experiment increased the knowledge base of how to treat high colour water in cold climates.
This experiment determined that conventional treatment of water at near-freezing temperature is possible, however the coagulant dosage needs to be increased so that good flocs can form. The good flocs formed are able to settle to the bottom of the beaker producing clear water at the sample tap level and to the water surface in the beaker.